This invention relates to electrical machines such as motors and generators, and particularly to bars which form part of the windings on large electrical machines as well as methods for producing such bars.
The windings of large electrical machines possess series connected rods whose cross sections are divided into mutually insulated single or individual conductors. This serves to reduce the additional current-produced heat losses. The individual conductors are twisted about each other at least over the entire length of the iron portion so that each partial conductor undergoes at least one complete helical turn, i.e., a 360.degree. turn of uniform pitch, while passing through a groove. In this manner all single or individual conductors interlink with equally large fluxes transverse to the groove. Only the current caused heat losses resulting from the small height and width of the single conductors, which may, for example, be in the form of Roebel rods, remains.
In conventional copper conductors of rectangular cross section this structure results in cross-overs of the single or individual conductors and in conductor bundles having cross-sections of varying configurations, particularly at the narrow sides of the conductor bundles or packs. This is particularly characteristic of a conventional bar structure, where the conductors pack is cooled by means of interspersed hollow conductors, because these hollow conductors often have larger cross sections than the solid conductors.
Prior to applying the principal or main insulation, it is therefore necessary to use suitable measures to make sure that the conductor bundle is rectangular over the total length of the bar. Failure to apply the insulation with adequate air exclusion, can cause internal discharges due to high operational electric fields. The resulting gaps occurring on the narrow sides of the single or individual conductor cross-over regions must be filled with a suitable filler material (i.e. white zinc bakelite paste or pigmented epoxy resin) so that the bar insulation (is applied) without air entrapment in the bar. See the book by Wiedemann and Kellenberger, entitled "Konstruktion Electrischer Machinen", published by Springer 1967, page 292. The surface of the conductors is often painted with resins containing fillers to fill in all remaining irregularities and to make possible substantially airless installation of the principal or main insulation. See the book by Sequenz, entitled "Herstellung der Wicklungen Electrischer Machinen", published by Springer 1973, page 148. However, only small irregularities can be filled in this manner. Therefore, a structure devoid of air pockets is not normally practical.
It is also possible to fill in irregularities on the narrow sides or edges of the bar windings with wedges of solid insulation material. This method is also suitable for filling larger surface notches. However fitting wedges into a large number of notches is very uneconomical and difficult to do.
It is therefore an object of the invention to produce a bar-winding with twisted single or individual conductors for electrical machines, and a process for its manufacture which avoids the disadvantages of known windings and methods.
Another object of the invention is to produce a better bar structure by means of a simplified and economical process.